EP2537059A1 - Auto-focus controlling apparatus, electronic imaging apparatus and digital still camera - Google Patents
Auto-focus controlling apparatus, electronic imaging apparatus and digital still cameraInfo
- Publication number
- EP2537059A1 EP2537059A1 EP11732985A EP11732985A EP2537059A1 EP 2537059 A1 EP2537059 A1 EP 2537059A1 EP 11732985 A EP11732985 A EP 11732985A EP 11732985 A EP11732985 A EP 11732985A EP 2537059 A1 EP2537059 A1 EP 2537059A1
- Authority
- EP
- European Patent Office
- Prior art keywords
- lens position
- focus
- lens
- focus lens
- evaluation value
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
Links
Classifications
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
- G02B7/28—Systems for automatic generation of focusing signals
- G02B7/36—Systems for automatic generation of focusing signals using image sharpness techniques, e.g. image processing techniques for generating autofocus signals
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B7/00—Mountings, adjusting means, or light-tight connections, for optical elements
- G02B7/28—Systems for automatic generation of focusing signals
- G02B7/36—Systems for automatic generation of focusing signals using image sharpness techniques, e.g. image processing techniques for generating autofocus signals
- G02B7/38—Systems for automatic generation of focusing signals using image sharpness techniques, e.g. image processing techniques for generating autofocus signals measured at different points on the optical axis, e.g. focussing on two or more planes and comparing image data
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B13/00—Viewfinders; Focusing aids for cameras; Means for focusing for cameras; Autofocus systems for cameras
- G03B13/32—Means for focusing
- G03B13/34—Power focusing
- G03B13/36—Autofocus systems
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- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03B—APPARATUS OR ARRANGEMENTS FOR TAKING PHOTOGRAPHS OR FOR PROJECTING OR VIEWING THEM; APPARATUS OR ARRANGEMENTS EMPLOYING ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ACCESSORIES THEREFOR
- G03B3/00—Focusing arrangements of general interest for cameras, projectors or printers
- G03B3/10—Power-operated focusing
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/60—Control of cameras or camera modules
- H04N23/67—Focus control based on electronic image sensor signals
- H04N23/673—Focus control based on electronic image sensor signals based on contrast or high frequency components of image signals, e.g. hill climbing method
Definitions
- the present invention relates to an improvement of an auto-focus controlling apparatus preferably used an electronic imaging apparatus or a digital still camera.
- an electronic imaging apparatus for example, a digital still camera has an auto-focus controlling apparatus (referred also to as an auto-focus adjustment apparatus) which converts a subject image into an image signal (image data) by an image pickup device
- an auto-focus controlling apparatus referred also to as an auto-focus adjustment apparatus
- CCD CCD
- a peak value scanning system (so-called climbing AF system or CCDAF system) is generally used, in which by calculating a peak value FVp in a hill-shaped characteristic curve MO acquired by focus evaluation values FV at lens positions fp of a focus lens fL, an optimum focus lens position fbp corresponding to the peak value FVp is acquired.
- the focus evaluation value FV is acquired by acquiring high frequency component of the image signal changed by driving the focus lens fL in an optical axis direction at discretely set lens positions fp.
- arrow Al indicates a case where the focus lens is driven in a direction from a lens position fp having a small value to a lens position having a large value to acquire the peak value FVp
- arrow A2 indicates a case where the focus lens is driven in a direction from a lens position fp having a large value to a lens position having a small value to acquire the peak value FVp.
- This peak value scanning system is a system for searching the optimum focus lens position fbp corresponding to a focusing state where there is lowest defocus by use of the actual image data and therefore the focus lens fL has a high focusing accuracy to the subject.
- this peak value scanning system since it is necessary to search the optimum focus lens position fbp while actually driving the focus lens, this peak value scanning system has a problem in that searching the optimum focus lens position fbp and setting the focus lens fL to the optimum focus lens position fbp take time.
- the conventional peak value scanning system in which a ranging sensor (referred also to as an external AF sensor) for directly measuring a distance to the subject is used, the distance to the subject is measured by the ranging sensor and based on a result of the ranging sensor, scanning at a vicinity of a lens position fp corresponding to the ranging result as a target lens position AFfp is performed so that high speed and high accuracy of the focusing control of the focus lens fL can be achieved (see Japanese Patent Application Publication Nos.2001-141984 and 2001-255451).
- a ranging sensor referred also to as an external AF sensor
- the focus lens fL is generally driven by a mechanical driving mechanism (see FIG.2) including a motor (pulse motor) driven by pulses and a gear.
- the lens position fp of the focus lens fL in the optical axis direction is determined by controlling a pulse number.
- the lens position when the focus lens fL is driven in the optical direction and in a direction of arrow Al as a normal direction and set to the optimum focus lens position fbp differs from the lens position when the pulse motor is rotated in a reverse direction and the focus lens fL is driven in a direction of arrow A2 and set to the optimum focus lens position fbp.
- the focus lens in order to detect a peak value FVp of the focus evaluation values FV, while the focus evaluation value FV increases, exceeds the peak value FVp and then decreases, for example, the focus lens is moved in the Al direction shown in FIG.3. Accordingly, when the peak value FVp of the focus evaluation values FV is determined by the calculation, the present lens position frp of the focus lens fL exceeds the optimum focus lens position fbp and is positioned at the end lens position fep' having the focus evaluation value FV smaller than the peak value FVp.
- the focus lens fL is returned back in the A2 direction and then, by a pulse number required for driving the focus lens fL from a corrected lens position fqp to the optimum focus lens position fbp, the pulse motor is driven to move the focus lens fL in the Al direction from the corrected lens position fqp to the optimum focus lens position fbp to set the focus lens fL to the optimum focus lens position fbp.
- a focal depth at a telephoto side is small compared to a focal depth at a wide angle side. Accordingly, a scanning range for scanning a peak value by moving the focus lens fL at the telephoto side is larger than that at the wide angle side.
- the pulse number for driving the focus lens fL toward another lens position fp is increased to reduce the time required for scanning.
- An object of the present invention is to provide an auto-focus controlling apparatus, an electronic imaging apparatus and a digital still camera, in which a time required from when the focus evaluation value is acquired by driving the focus lens to when completing the focusing the focus lens on the subject is reduced.
- An auto-focus controlling apparatus is for controlling a focusing operation of a focus lens and includes a focus evaluation value generating device configured to generate a focus evaluation value based on image data of a subject which is acquired through the focus lens to determine a focus lens position of the focus lens to the subject, a target lens position determining device configured to determine a target lens position used in the focusing operation by driving the focus lens, a focus evaluation value acquiring timing determining device configured to determine a plurality of acquisition lens positions in which the focus evaluation values are to be acquired in a direction from a present lens position of the focus lens toward the target lens position, a scanning device configured to drive the focus lens in an optical axis direction and in the direction from the present lens position of the focus lens to the target lens position to acquire the focus evaluation value at each of the plurality of acquisition lens positions, a predicted focus lens position determining device configured to predict a predicted focus lens position based on the acquired focus evaluation values to determine the predicted focus lens position, and a moving device configured to stop the scanning device to drive
- FIG.l is an explanatory view schematically showing an example of a conventional peak value scanning system.
- FIG.2 is an explanatory view schematically showing a backlash existing in a mechanical driving mechanism.
- FIG.3 is an explanatory view schematically showing procedures to complete focusing of a focus lens by the conventional peak value scanning system.
- FIG.4 is a block circuit diagram including an optical system of the digital still camera according to an embodiment of the present invention.
- FIG.5 is an explanatory view schematically showing a relationship between main processings and parallel processings of the digital still camera according to an embodiment of the present invention.
- FIG.6 is a flowchart for explaining the main processings of the digital still camera according to an embodiment of the present invention.
- FIG.7 is a flowchart of a focus evaluation value acquiring timing determining processing shown in FIG.6.
- FIG.8 is a supplementary explanatory view showing processing procedures of the focus evaluation value acquiring timing determining processing shown in FIG.7.
- FIG.9 is a flowchart of a scanning processing shown in FIG.6.
- FIG.10 is a view showing a relationship among a focus evaluation value generating timing shown in FIG.7, a vertical synchronization timing, an exposure timing, an evaluation value interrupt timing, and a control of a pulse motor.
- FIG.11 is a flowchart of an evaluation value interrupt processing shown in FIG.5.
- FIG.12 is a graph showing a relationship between an optimum focus lens position acquired by the conventional peak value scanning system and a predicted focus lens position acquired by a scanning system according to an embodiment of the present invention.
- FIG.13 is a view showing numeric values of the focus evaluation values acquired at the acquisition lens positions shown in FIG.12.
- FIG.14 is a flowchart for explaining another example of the evaluation value interrupt processing shown in FIG.11
- FIG.15 is a correction factor characteristic curve according to an embodiment of the present invention.
- FIG.4 is a block diagram schematically showing a circuit configuration of a digital camera, which is capable of recording a still image, as an electronic imaging apparatus having an auto-focus controlling apparatus according to an embodiment of the present invention.
- fL indicates a focus lens
- 2 an aperture-mechanical shutter which also has a function of an aperture
- 3 an image pickup device (CCD)
- 4 an FE-IC 102 circuit section
- 5 a digital still camera processor (DSP) section
- 6 a driver section
- 7 a CCD driving circuit section
- 8 a central processing unit (CPU)
- 9 an embedded memory
- 10 a communication driver circuit section
- 11 a memory card
- 12 a display section 13 a switch section
- 14 a ranging sensor (external AF)
- 15 a strobe light emitting section
- 16 a main capacitor
- 17 a strobe light receiving section.
- the FE-IC 102 circuit 4 has a well-known function of performing a correlated double sampling of an image signal from the image pickup device 3, a function of performing an automatic gain control (AGC), and a well-known function of converting image signal acquired by the image pickup device 3 into image data, that is, an A/D converting function.
- the digital still camera processor section 5 has a function of converting digital signals (imaging signal after performing an A/D conversion) into YUV data, and a function of performing a processing of digital signals, that is, a JPEG-compression of the YUV data, and the like.
- the driver section 6 includes a mechanical driving mechanism as a scanning device configured to drive the focus lens fL in an optical axis direction in cooperation with the CPU 8, and a shutter driving mechanism configured to drive the aperture-mechanical shutter 2 to be opened and closed.
- a mechanical driving mechanism as a scanning device configured to drive the focus lens fL in an optical axis direction in cooperation with the CPU 8, and a shutter driving mechanism configured to drive the aperture-mechanical shutter 2 to be opened and closed.
- a well-known lens position detecting section is provided in the mechanical driving mechanism.
- the mechanical driving mechanism generally comprises a not-illustrated pulse motor and a gear lines similarly to the conventional mechanism.
- the pulse motor is controlled to be driven by a pulse output from the CPU 8 as a moving device and the focus lens fL is controlled to be driven by a pulse from the CPU 8.
- the CCD driving circuit section 7 drives the image pickup device 3 to output an image signal to the FE-IC 102 circuit section 4 based on synchronization signals (vertical synchronization signal VS and horizontal synchronization signal HS) from the CPU 8.
- the CPU 8 operates overall controls of functions of the digital still camera as a whole.
- the embedded memory 9 has a function of temporarily storing image data acquired by the image pickup device and read data stored in the memory card 11.
- the embedded memory 9 is also used as a working memory of the digital still camera processor section 5 and the CPU 8.
- the memory card 11 is attachably and detachably installed in the digital still camera.
- the communication driver circuit 10 is used for communicating with an external device such as a personal computer, a printer, and the like.
- the displaying device 12 is composed of a not-illustrated liquid crystal display and a not-illustrated display controller section configured to convert the image data from the digital still camera processor section 5 into a signal to be displayed on the liquid crystal display.
- the switch section 13 includes various switches, such as a shutter button required to operate the digital still camera, a mode dial, a wide angle/telephoto zoom switch, a self-timer switch, a menu switch, a strobe switch, and the like.
- a user of the digital still camera operates the switch section 13 to perform a desired processing of the digital still camera.
- SW1 indicates a first switch of the shutter button
- SW2 indicates a second switch of the shutter button.
- the ranging sensor 14 is configured to measure a distance to a subject by performing a ranging based on a so-called triangulation method.
- a floodlight type method a passive type method for measure a distance to the subject based on a defocus amount to the subject, or a sonar detection method may be used.
- the strobe light emitting section 15 is controlled to emit the light based on a control signal from the CPU 8.
- the main capacitor 16 reserves an electrical power for emitting strobe light.
- the CPU 8 has a function of monitoring a charging voltage of the main capacitor 16.
- the strobe light receiving section 17 is composed of a light receiving optical system, a light-receiving sensor, and a light emitting stop circuit section, which are not illustrated.
- the CPU 8 outputs a light receiving command signal to the strobe light receiving section 17 and outputs a setting value signal for stopping light emitting to the strobe light receiving section 17.
- the light-receiving sensor starts to receive light based on the light receiving command signal from the CPU 8 and when an accumulated receiving light amount runs to a setting value, the light emitting stop circuit section outputs a light emitting stop signal to the strobe light emitting section 15.
- the CPU 8 performs main processings and parallel processings shown in FIG.5 in cooperation with processing devices such as the digital still camera processor section 5, the driver section 6, the image pickup device 3 and the like.
- the main processings are, for example, a switch state judging processing (SW judging processing) for judging a switch state, an exposure evaluation value acquiring processing (focus evaluation value generating means (AE processing)) for acquiring an exposure evaluation value, a ranging processing (referred also to as an external AF processing) for calculating a distance to the subject based on a ranging result acquired by the ranging sensor 14, a focus evaluation value acquiring timing determining processing (focus evaluation value acquiring timing determining means) for determining a timing of acquiring a later-described focus evaluation value FV, a scanning processing (referred also as to a scanning means (CCDAF processing)) for discretely acquiring the focus evaluation value FV by actually driving the focus lens fL, and a focus evaluation value reliability judging processing (judging means) for judging a reliability of a later-de
- the parallel processings are interrupt processings which are performed while the main processing is performed.
- the parallel processings are particularly, a periodic interrupt processing, a monitoring processing for monitoring a subject image before photographing the subject, an evaluation value interrupt processing for changing a speed of the pulse motor by judging whether or not the focus evaluation value FV is acquired during the scanning processing (CCDAF) by driving the focus lens fL as well as for calculating a predicted focus lens position fp", and a motor control interrupt processing for performing a speed control of a driving speed of the pulse motor and a stop control of the pulse motor.
- CDAF scanning processing
- the parallel processings will be described below.
- Information transfer is performed between processing information of the parallel processings and processing information of the main processings, as shown by arrows in FIG.5, and therefore the processing information is sequentially updated.
- FIG.5 is an explanation view schematically showing a relationship between the main processings and the parallel processings.
- the monitoring processing is periodically performed. Periodic interruption processing will be explained.
- the periodic interrupt processing is activated by a periodic timer and then, for example, processing for allowing the CPU 8 to read the switch state of the switch section 13 shown in FIG.4 is performed.
- the evaluation value interrupt processing is performed when the image data acquired based on an exposure for each vertical synchronization signal VS is processed and then the exposure evaluation value (AE evaluation value) is generated.
- the motor control interrupt processing is permitted after parameters of the driving speed for controlling the pulse motor and the target lens position AFfp are set during the scanning processing in the main processings.
- An interrupt is generated at a driving timing corresponding to control phase of the pulse motor after the interrupt processing is started and the motor control interrupt processing is performed at the timing when the interrupt is generated.
- driving parameters are checked and the control is changed so as to correspond to the change in the driving parameters.
- a still image recording mode when the power of the digital still camera is turned on, an initialization of a not-illustrated hardware in the digital still camera, an initialization where file information in the memory card 11 is formed in the embedded memory 9, and the like are performed and then the main processings shown in FIG.6 are performed.
- a monitoring state is checked (S.l), and if the monitoring state is a monitoring stop state, a monitoring start processing is performed (S.2).
- the monitoring start processing is a processing for starting to drive the image pickup device 3 and activate the monitoring processing in the parallel processings. Also, when the processing flow returns to the first step S.l. as shown in FIG.6 while the parallel processings other than the monitoring processing are performed, the monitoring start processing is performed (S.2).
- the digital still camera processor section 5 outputs the image signal acquired by the image pickup device 3 to the display section 12 (see FIG.4). Thereby, a through image (moving image) is displayed on the liquid crystal display of the display section 12.
- the digital still camera processor section 5 performs a tracking processing by calculating an exposure amount evaluation value AE and a white balance evaluation value AWB based on the image signal from the image pickup device 3.
- the CPU 8 receives the above evaluation values and outputs a control signal to a not -illustrated timing generator (TG generator) of the CCD driving circuit section 7 so as to set the evaluation values to be predetermined values and thereby, an electronic shutter driving timing (electronic shutter time) of the image pickup device (CCD) 3 is set.
- TG generator not -illustrated timing generator
- the monitoring processing coloring and brightness of the through image is maintained appropriate.
- the monitoring processing is performed, for example, by a periodic timer interrupt processing every 20 ms.
- the electronic shutter of the image pickup device 3 has a maximum time and minimum time within a settable time. That is, electronic shutter driving time of the CCD has an upper limit and a lower limit.
- the CPU 8 controls the driver section 6 to be driven to change a diameter of the aperture of the aperture -mechanical shutter section 2 or controls the automatic gain control (AGC) function of the FE-IC102 circuit section 4 to change an amplification factor of the image signal so as to acquire an appropriate exposure amount.
- AGC automatic gain control
- the CPU 8 performs a feedback control for adjusting a color parameter by image processing of the digital still camera processor section 5. That is, the CPU 8 performs an adjusting processing of the parameter of the white balance evaluation value AWB.
- the CPU 8 judges a state of the switch section 13 during monitoring (S.3).
- the judgment of the state by the CPU 8 is performed based on reading of the switch state of the switch section 13 on the CPU 8.
- the reading processing of the switch state of the switch section 13 on the CPU 8 is also performed by the periodic timer interrupt every 20 ms.
- the CPU 8 judges switch information input by the periodic timer interrupt processing every 20 ms.
- the CPU 8 judges whether or not the first switch (half-pressed switch) SW1 of the shutter button of the switch section 13 is turned on in the step S.3.
- the CPU 8 performs the processings of S.4 to S.ll. If the first switch SW1 is turned off, the CPU 8 judges whether or not the switches other than the first switch SW1 in the switch section 13 is operated. The CPU 8 performs a processing corresponding to the operated switch (S.12). If no switch is operated during performing the main processings as a loop processing, the processing flow returns to the step S.l and the CPU 8 performs the main processings as a loop processing.
- a strobe photographing mode is selected, after the monitoring start processing is performed (S.2), it is checked whether a strobe charging is completed. After a not-illustrated charging start processing is performed if the charging is required, the state judging processing of the switch section is performed (S.3) but the explanation is omitted.
- the CPU 8 performs the monitoring stop processing (S.4) and then performs the exposure value evaluation processing (AE processing) (S.5).
- AE processing the exposure amount evaluation value is acquired and the exposure time of the image pickup device 3 is set as well as the amplification factor of the automatic gain control (AGO being set.
- the CPU 8 when photographing the still image, if the first switch SW1 of the shutter button is turned on, the CPU 8 performs the AE processing in cooperation with the digital still camera processor section 5 to evaluate the image data and determine an exposure time value of the image pickup device 3 to be set and an amplification factor of the image signal to be set in the CCD driving circuit section 7.
- the CPU 8 performs the ranging processing by the ranging sensor 14 (S.6).
- the ranging sensor external AF sensor 14
- triangulation method is generally used and such a ranging sensor 14 is disclosed in Japanese Patent Application Publication No.2001-255451 and therefore the detailed explanation is omitted.
- the embedded memory (adjust memory) 9 a relationship between a ranged value acquired by the ranging sensor 14 and a target lens position AFfp based on the ranged value is stored.
- the CPU 8 calculates the target lens position AFfp with reference to an adjusting value based on the ranging result by the ranging sensor 14.
- the focus evaluation value acquiring timing determining processing is performed in line with a program of the CPU 8.
- a scanning range (driving range in an optical axis direction) of the focus lens fL in performing the scanning processing for acquiring the focus evaluation value FV by driving the focus lens fL is set to a range at a vicinity of the target lens position AFfp to be scanned.
- the focus lens fL can be rapidly positioned to a vicinity of an optimum focus lens position fbp.
- the focus evaluation value acquiring timing determining processing will be explained as a processing for determining the lens position fp for acquiring a focus evaluation value.
- the processing may be for determining a timing of acquiring a focus evaluation value based on a time for acquiring the focus evaluation value.
- a lens position fp for acquiring the focus evaluation value that is, a start lens position, an intermediate position, and an end lens position for acquiring the focus evaluation values indicate a acquisition lens position fp', that is, fsp', fp', and fep', respectively.
- the start lens position fsp' is a first lens position for starting to acquire the focus evaluation value
- the intermediate lens position fp' is a lens position fp between the start lens position fsp' and the end lens position fep'
- the end lens position fep' is a lens position fp where the focus evaluation value is finally acquired.
- These lens positions are lens positions fp for acquiring the focus evaluation values and therefore referred also to as the acquisition lens positions fp'.
- the target lens position AFfp is a lens position fp which is determined based on a ranging value acquired by the ranging sensor 14, and the optimum focus lens position fbp is a lens position fp which is calculated by a peak value FVp in a hill-shaped characteristic curve MO.
- the CPU 8 sets an array ScfpD for determining lens positions fp' for acquiring focus evaluation values.
- the number of elements indicating an array number of the array ScfpD is appropriately changed.
- the number n of elements is one hundred.
- the lens position fp' is sequentially stored.
- the start lens position fsp', the end lens position fep' and the intermediate lens positions fp' between the start lens position fsp' and the end lens position fep' are stored based on a present lens position frp of the focus lens fL.
- the start lens position fsp' is stored in the array ScfpO of the maximum number array
- the end lens position fep' is stored in the array Scfp[0] of the minimum number array.
- the end lens position fep' is determined by the target lens position AFfp.
- the end lens position fep' is set to be equal to the target lens position AFfp.
- the end lens position fep' is changeable during the later-described processing according to properties of the acquired focus evaluation value.
- the target lens position AFfp is assumed as 109
- the end lens position fep' is 109.
- a number "2" indicates two-pulses driving of the pulse motor. That is, the focus evaluation value FV is acquired at the acquisition lens position fp' every driving with an interval of two pulses. The focus evaluation value FV is acquired at the acquisition lens position fp' of the focus lens fL every two pulses as the interval.
- the lens positions are positioned with fine intervals at a vicinity of the optimum focus lens position fbp and therefore an accuracy for detecting the peak of the focus evaluation value FV is improved.
- the end lens position fep' is 109 and therefore the acquisition lens position fp' stored in the array Scfptl] is 107.
- the present lens position frp of the focus lens fL is compared with the reference lens position fp' stored in the array Scfp[n] at the present time (S.24).
- the present lens position frp of the focus lens fL is smaller than the acquisition lens position fp' stored in the array Scfp[n] at the present time, it is judged as "No” and then it is judged whether or not the variable n is smaller than 2 (S.25).
- the acquisition lens position fp' acquired at the previous time is "107", and therefore "105" is stored in the array Scfp[2].
- the present lens position frp of the focus lens fL is compared with the acquisition lens position fp' acquired at this time and stored in the array Scfpin] (S.24). If the present lens position frp of the focus lens fL is smaller than the acquisition lens position fp' stored in the array Scfp[n] at the present time, it is judged as "No", and then judges whether or not the variable n is smaller than 2 (S.25).
- the present lens positon frp is compared with the acquisition lens position fp' stored in the array Scfp[n] at the present time. This is because, three acquisition lens positions fp' cannot be acquired if the interval between the optimum lens position fbp and the present lens position frp is finely defined by driving the pulse motor every two pluses and three focus evaluation values FV with the interval of two pulses are acquired, and further the interval between the optimum focus lens position fbp and the present lens position frp is smaller than a five-pulses interval.
- a number "4" indicates four-pulses driving of the pulse motor. That is, the focus evaluation value FV is acquired at the acquisition lens position fp' every driving with an interval of four pulses.
- the focus evaluation value FV is acquired at the acquisition lens position fp' of the focus lens fL every four pulses as the interval. This is because the focus lens fL is rapidly moved close to the optimum focus position fbp.
- the present lens position frp of the focus lens fL is compared with the acquisition lens position fp' stored in the array Scfptn] at the present time (S.28).
- the CPU 8 judges whether or not the variable n is smaller than 100 (S.29).
- the CPU 8 judges whether or not the variable n is smaller than 100 (S.29).
- the CPU 8 sets the variable n-1 to the variable n (S.30), and the lens position timing determining processing for acquiring a focus evaluation value is completed.
- the lens position "97" stored in the array Scfp[4] is determined as the start lens position fsp'.
- the acquisition lens positions are determined from a position having a large number to a position having a small number.
- the flowchart shown in FIG.7 of the focus evaluation value acquiring timing determining processing is explained as a processing under the condition where the present lens position frp is smaller than the target lens position AFfp, for convenience of the explanation.
- the present lens position frp is equal to or more than the target lens position AFfp
- the judging conditions of S.24 and S.28 are reversed and the intervals in the steps S.23 and S.27 are set to four pulses to be increased and therefore the explanation is omitted.
- a scanning direction of the focus lens fL corresponds to a direction shown by arrow A2 in FIG.l.
- the lens positions fp are determined from a position having a small number to a position having a large number.
- the CPU 8 performs a error processing if the present lens position frp is smaller than the lens position fp' acquired at this time even when the processings of the steps S.27 to S.29 are repeated one hundred times.
- the explanation of the error processing is omitted.
- the CPU 8 After the CPU 8 performs the focus evaluation value acquiring timing determining processing (S.7), the CPU performs the scanning processing (the step S.8 in FIG.6) for acquiring the focus evaluation value FV by actually driving the focus lens fL.
- the focus lens fL is driven with the four pulse interval and the focus lens fL is driven with two pulse interval at the vicinity of the end lens position AFfp so that the focus evaluation value FV can be rapidly acquired.
- the focus evaluation value FV is finely acquired at the vicinity of the target lens position AFfp so that the accuracy of detecting the focus position can be improved.
- pulse interval is used for driving the focus lens fL according to the image processing system including an optical system of the digital still camera and it is preferably determined mainly in accordance with a focal depth of the focus lens fL.
- a memory CCDAFmode for judging a scanning mode is prepared and a flag "1", a flag "2", and a flag “3" are prepared.
- the flag “1” indicates a focus predicting mode
- the flag "2” indicates a conventional peak value scanning mode
- the flag "3” indicates a predetermined position mode. The set of the flags "2" and “3” will be later described.
- the CPU 8 performs a scanning start processing (S.32).
- a parameter of interrupt of a motor control timer interrupt processing are set at timings corresponding to the present lens position frp, the start lens position fsp' in the array Scfp[n] determined in the focus evaluation value acquiring timing determining processing (S.7 in FIG.6), the intermediate lens position fp' and the end lens position fep', and the motor control timer interrupt is permitted.
- the driving of the pulse motor is started and the focus lens fL is actually driven, for example, in a direction of arrow Al.
- the CPU 8 judges whether or not the scanning is completed (S.33).
- the step S.33 is repeated until the scanning is completed.
- This loop of S.33 is referred to as a scanning processing stop waiting loop, hereinafter.
- the processing flow directly moves to the switch state judging processing (see S.9 in FIG.6).
- FIG.10 shows a relationship among the lens position fp of the focus lens fL by the motor control, the vertical synchronization signal VS, an exposure timing, a focus evaluation value generating timing, and the evaluation value interrupt timing.
- the acquisition lens position fp' determined by the focus evaluation value acquiring timing determining processing is as follows:
- a time in which the vertical synchronization signal VS every four pulses is acquired is acquired, a time in which the vertical synchronization signal VS every two pulses is acquired are required.
- the CPU 8 calculates a timing for acquiring the focus evaluation value FV in each lens position fp and sets an interrupt timer after the initial excitation at the timing synchronized with the vertical synchronization signal VS.
- the CPU 8 After the CPU 8 sets the start lens position fsp', the intermediate lens position fp' and the end lens position fep', the CPU 8 permits the motor control interrupt processing.
- the interrupt is generated at the initial excitation time tO and then the timer interrupt is generated at an interval based on the driving speed. Thereby, the pulse motor is driven every one pulse.
- the motor control interrupt processing refers again to the driving parameters set by the other processing every interrupt. Thereby, the driving speed of the pulse motor, the end lens position fep' where the focus lens is to be stopped are appropriately switched.
- the scanning start processing permits the evaluation value interrupt processing (predicted focus lens position determining device) shown in FIG.11.
- the focus evaluation value FV is acquired, for example, as follows.
- the digital still camera processor section 5 performs three tap digital filter processing of -1/2, 1, 1/2 on the brightness data of digital pixel data of the image signal in a horizontal scanning direction during the pulse motor driving processing to detect a high frequency component.
- the digital still camera processor section 5 accumulates output values acquired by the filtering processing over pixels occupying an area of 1/4 of a center of a screen of the liquid crystal.
- the generation of the focus evaluation value FV is completed at a timing of rising the vertical synchronization signal VS, and then the evaluation value interrupt processing shown in FIG.11 is started at the timing shown in FIG.10.
- the focus evaluation value generated in S.401 is acquired.
- the later-described predicting processing in S.402 is performed. If a prediction is OK, that is, a predicted focus lens position fp" is acquired in the predicting processing, the processing flow moves to S.420 and the present lens position frp is compared with the predicted focus lens position fp". If the present lens position frp is not more than the predicted focus lens position fp", the processing flow moves to S.421 and a target position where the focus lens is to be stopped is changed to the predicted focus lens position fp". The processing flow moves to S.422 and an evaluation value interrupt inhibit processing for inhibiting the evaluation value interrupt processing is performed to escape from the evaluation value interrupt processing and the processing flow returns to S.33.
- the prediction is NG, that is, the predicted focus lens position fp" is not acquired by the predicting processing, it is judged whether or not the present lens position frp is the acquisition lens position fp' stored in the array Scfp[2] (S.405).
- the present lens position frp of the focus lens fL is changed and the processing flow moves again to the evaluation value interrupt processing shown in FIG.ll.
- the processing flow returns to S.33 in FIG.9, and the pulse motor is continuously driven.
- the focus evaluation value FV at the end lens position fep' stored in the array ScfptO] is acquired.
- the predetermined lens position is used when the automatic focus detection cannot be performed and the lens position which is preliminarily determined based on a zooming position in a photographing device, and the like.
- CCDAFmode 2
- the focus prediction scanning mode is canceled and it is judged that the focus lens fL is positioned at the lens position fp which exceeds a lens position having the peak value FVp of the focus evaluation values FV.
- the overrun correction control processing of the focus lens fL is performed to return the focus lens fL to the optimum focus lens position fbp corresponding to the lens position having the peak value FVp of the focus evaluation values FV.
- the image pickup device 3 is exposed every vertical synchronization signal VS and the data transfer processing of the image pickup device 3, the focus evaluation value generating timing processing, and the focus evaluation value interrupt processing are performed for a transferring period from when the present vertical synchronization signal VS is generated to when the next vertical synchronization signal is generated.
- a driving control of the pulse motor is started such that the acquisition lens position fp' for acquiring a focus evaluation value of ScfpD, which is acquired by the focus evaluation value acquiring timing determining processing is matched with a timing of rising the vertical synchronization signal VS.
- the focus evaluation value FV is generated in synchronization with the timing of rising the vertical synchronization signal VS.
- the CPU 9 has a function as a predicted focus lens position predicting device.
- FIG.12 is a graph showing a relationship between the lens position fp and the focus evaluation value FV when the scanning processing is performed.
- the lens position fp is used as a lens including the present lens position frp, the start lens position fsp', the end lens position fep', the intermediate lens position fp' between the start lens position fsp' and the end lens position fep', the target lens position, the optimum focus lens position fbp, and the predicted focus lens position fp".
- broken line indicates a characteristic curve MO having a maintain shape of the focus evaluation values FV acquired on the assumption that the focus lens fL can be set to the lens position fp in the optical axis direction by controlling the focus lens fL in a nonstep manner to the subject. It is also shown as the characteristic curve in a case where the focus lens fL is in a defocused state to the subject.
- the lens position fp of the focus lens fL is controlled not with the non step control but also stepwisely controlled with a stepwise control by the pulse motor, and a control capability of the focus lens fL is finite.
- sampling of the focus evaluation value information is performed only at the discretely separated lens positions fp.
- the characteristic curve MO of the focus evaluation values FV can be acquired.
- a determining method for determining the prediceted focus lens position fp" according to this Example is explained with reference to an example compared to the conventional determining method for determining the optimum focus lens position fbp.
- the ranging accuracy of the ranging sensor 14 is, for example, in a case of the triangulation method, a fixed accuracy determined by a base-line length and a focal length of an automatic focus (AF) optical system. Accordingly, the ranging accuracy is not sufficient for a telephoto lens, and the like.
- the ranging error corresponds to, for example, about 8 pulses
- the optimum focus lens position fbp can be effectively searched even when the ranging error by the ranging sensor exists.
- the focus evaluation value FVp of the focus evaluation values FV when the peak value FVp of the focus evaluation values FV is detected, in order to avoid error detection of the peak value FVp based on influence of noise due to the circuits of the digital still camera and noise due to the photographing image, it is judged that there is no detection error in the detection of the peak value FVp of the focus evaluation values FV, if the focus evaluation value FV acquired at this time is smaller than the focus evaluation value FV acquired at the previous time and when a focus evaluation value FV to be acquired at the next time is set as the focus evaluation value FV acquired at the present time, the focus evaluation value FC acquired at the present time is smaller than the focus evaluation value FC acquired prior to the previous time.
- the focus evaluation values FV acquired as described above are shown by filled square in FIG.12.
- the CPU 8 calculates the peak value FVp of the focus evaluation values FV from the characteristic curve MO and calculates the optimum focus lens position fbp from the peak value FVp.
- the focus lens fL is driven until the focus evaluation value FV exceeds the peak value FVp. Accordingly, in order to acquire the subject image without defocus, after once the focus lens fL is driven in a reverse direction, the focus lens fL is driven again in a normal direction to be positioned at the optimum focus lens position fbp.
- the focus lens fL is driven in the optical axis direction in order of several micrometers for one pulse. Accordingly, if there is backlash of 0.01 mm, the error due to backlash corresponds to several pulses. Then, if a backlash amount changes due to part accuracy and assembling error, the pulse number also largely changes due to the changed amount in terms of pulse number, so that the pulse number cannot be used as the fixed difference.
- the focus lens fL is driven in the scanning direction (Al direction) from the present lens position fp and driving of the pulse motor is once stopped at the end lens position fep'.
- the pulse motor is excited and the focus lens fL is driven in the reverse direction (A2 direction) from the end lens position (lens stop position) fep' by sum of the pulse number corresponding to the difference between the end lens position fep' and the optimum focus lens position fbp and the pulse number corresponding to the error due to backlash, and then driving of the pulse motor is stopped. Thereby, the focus lens fL is stopped at a corrected lens position fqp.
- the pulse motor is excited again and the focus lens fL is driven from the corrected lens position fqp to the optimum focus lens position fbp in the Al direction.
- an interval between the vertical synchronization signals is 16 ms.
- the time required for acquiring one focus evaluation value FV is, as shown in FIG.10, 16 ms as a maximum.
- the driving speed of the focus lens fL is 16 ms to the four lens positions fp and therefore a time required for changing one lens position fp is 4 ms. It is assumed that a stop excitation time tO is 10 ms.
- the stop excitation time tO is 10 ms.
- the focus evaluation values FV at the acquisition lens positions are indicated by a triangles.
- a slope of the evaluation values is calculated at each acquisition lens position.
- a difference value "894" for four pulses is calculated.
- a difference value "354" is calculated.
- a difference value "276" is calculated.
- the predicting processing is to perform the focus predicting processing by use of the two decreased values of the acquired slopes, that is, 354, and 276.
- a decreased ratio of the two decreased data is defined by " (second decreased data) / (first decreased data) x 100 (%).
- “276'T354"xl00 78 (%)
- the lens position fp calculated by the linear interpolation formula is corrected.
- the correction is performed by use of a correction ratio characteristic curve shown in FIG.15.
- a correction input value is the decreased ratio of the slope and a correction output value is a correction ratio to a number of a pulse interval for acquiring the evaluation value. If the decreased ratio is 0%, the slope of the second decreased data is almost zero, and the lens position calculated by the linear interpolation formula by use of the first and second decreased data has the slope of zero (no slope), that is, indicates a peak of the hill shape of the characteristic curve of the evaluation values and no correction is performed.
- the lens position of the second decreased data is far from the lens position having the slope of zero and the lens position calculated by the linear interpolation formula may have large error so that large correction is required.
- the decreased ratio is 78 % and the correction factor is -60% based on the correction factor characteristic curve.
- the lens position of 109 that is, the lens position at a close side is used for acquiring the predicted focus lens position fp".
- the focus lens is already driven over the lens position when the predicted focus lens position fp" is acquired.
- the focal depth range where the focus lens is apparently in a focusing state by an F value is previously stored in the photographing apparatus.
- the lens position where the focus lens is stopped after the predicted focus lens position fp" is acquired is compared with the predicted focus lens position fp".
- the focus lens is not required to be moved. Therefore, in the movement judging in S.37, it is judged that the focus lens is not required to be moved.
- the focus lens is required to be moved. Accordingly, in the movement judging in S.37, it is judged that the focus lens is required to be moved and therefore the focus lens is controlled to be moved to the predicted focus lens position fp".
- the driving speed of the focus lens requires 8 ms to change one acquisition lens position fp. Accordingly, the driving speed is lower than a driving speed in a case where the focus evaluation values FV are acquired every four pulses.
- the stop excitation time of the pulse motor is 10 ms. Accordingly, a total driving time of the focus lens fL is 86 ms.
- the time required from a scanning start to a scanning completion is short.
- the processing flow After completing the focusing, the processing flow returns to the main processing in FIG.6, and moves to S.9 to perform the switch state judging processing. If the first switch SWl is turned on, the processing flow moves to S.10 and if the second switch SW2 is turned on, the processing flow moves to S.ll.
- the focus evaluation value generating device generates the focus evaluation value based on the image data acquired through the focus lens to determine the focus lens position to the subject
- the target lens position determining device determines the target lens position as a target to perform the focusing operation by driving the focus lens
- the focus evaluation value acquiring timing determining device determines a plurality of acquisition lens positions each for acquiring the focus evaluation value in a direction from the present lens position of the focus lens toward a position where the target lens position exists
- the scanning device drives the focus lens in the optical axis direction and in a direction from the present lens position toward the position where the target lens position exists to acquire the focus evaluation value at each of the acquisition lens positions.
- the predicted focus lens position determining device predicts a focus lens position based on the focus evaluation values and if the predicted focus lens position is determined, the moving device stops the scanning device to drive the focus lens, and to drive the focus lens in the same direction as the direction where the focus lens is driven by the scanning device to move the focus lens to the predicted focus lens position.
- the predicted focus lens position determining device corrects the predicted focus lens position based on the decreased ratio calculated by slopes of the focus evaluation values to determine the corrected focus lens position as the predicted focus lens position.
- the focusing accuracy of the focus lens fL to the subject is low.
- the focus evaluation value FV acquired at each acquisition lens position for acquiring the focus evaluation value includes noise so that an accuracy of the focus evaluation values FV is degraded.
- the focusing accuracy of the focus lens fL to the subject may be degraded.
- the ranging accuracy of the ranging sensor 14 may be low. Since each acquisition lens position fp' is determined based on the target lens position AFfp by the ranging sensor 14, when the accuracy of the ranging sensor is low, the finally acquired predicted focus lens position fp" has low accuracy.
- a so-called climbing type scanning method in which the pulse motor drives the focus lens fL in one direction, the focus evaluation value FV is acquired at each of the acquisition lens positions fp' discretely set with an even interval from the start lens position fsp', it is judged twice whether the difference between the focus evaluation value FV at the present time and the focus evaluation value FV at the previous time is "+" (positive) or "-" (negative) to detect a peak of the focus evaluation values FV, if the two judging results are it is judged that the lens position exceeds a position having the peak.
- scanning of the focus lens fL is stopped when the judging result of "-" is acquired twice in series.
- the scanning processing during performing the prediction mode if the focus evaluation value FV acquired at the acquisition lens position fp' is smaller than a predetermined value, since the finally acquired predicted focus lens position fp" has low reliability, it is preferable to change the scanning processing from the prediction mode to the conventional mode during the scanning processing while performing the prediction mode.
- FIG.14 is a flowchart showing an example of the evaluation value interrupt processing including a reliability judging processing (judging device) for judging the reliability of the predicted focus lens position fp" and a mode switching processing.
- the present lens position frp is not the acquisition lens position fp' stored in the array Scfp[2], it is judged as "No", and the it is judged whether or not the present lens position frp is the end lens position fep' stored in the array Scfp[0] (S.54).
- the processing flow moves to S.503 and the present lens position frp is compared with the predicted focus lens position fp". If the present lens position frp does not exceed the predicted focus lens position fp", the processing flow moves to S.505 and the target position where the focus lens is to be stopped is changed to the predicted focus lens position fp". Then, the processing flow moves to S.506 to perform the evaluation value interrupt inhibit processing and the processing flow escapes from the evaluation value interrupt processing and returns to S.33.
- the processing flow moves to S.504 and a lens stop switching processing for stopping the focus lens is performed. Then the processing flow moves to S.506 to perform the evaluation value interrupt inhibit processing and then the processing flow escapes from the evaluation interrupt processing and returns to S.33.
- the processing flow moves to S.55 and it is judged whether or not the focus evaluation value FV acquired at the present lens position frp is smaller than the predetermined value.
- the focus evaluation value FV at the acquisition lens position fp' stored in the array Scfp[3] is used as the predetermined value. This is because, if the focus evaluation value FV at the acquisition lens position fp' stored in Scfp[3] is a predetermined level or less, a contrast component of the subject is small even at the vicinity of the optimum focus lens position fbp.
- the noise judging for example, it is judged that the changing direction is an increased direction if the difference between the focus evaluation value FV acquired at this time and the focus evaluation value FV acquired at the previous time is "+” and the changing direction is a decreased direction if the difference between the focus evaluation value FV acquired at this time and the focus evaluation value FV acquired at the previous time is If the changing direction acquired at the present time is different from the changing direction acquired at the previous time, "+1" is counted as a count and then an index value m/M indicating noise amount, where m is a sum of the counted values as a numerator and M is an acquired number of acquiring times of the focus evaluation values as a denominator.
- the focus evaluation value FV at the start lens position fsp' stored in Scfp[4] and the focus evaluation value FV at the acquisition lens position fp' stored in Scfp[3] in the predicting processing are acquired.
- the present lens position frp of the focus lens fL reaches the acquisition lens position stored in the array Scfp[2], and then the focus evaluation value at the acquisition lens position stored in the array Scfp[2] is acquired.
- the processing flow moves to S.509 and it is judged whether or not the ov value is 5 or more. Thereby, while it is not judged as "OK" in the predicting processing, the initial ScfptO] is updated up to five times to control the lens position.
- the CPU 8 sets the acquisition lens position fp' as the lens position fp where the focus lens is driven from the present lens position frp by four pulses (S.61).
- the processing flow moves to S.62 and it is judged whether or not the focus evaluation value FV acquired at the acquisition lens position fp' at the present time is smaller than the focus evaluation value FV acquired at the acquisition lens position fp' at the previous time.
- the focus evaluation value FV acquired at the acquisition lens position fp' at the present time is larger than the focus evaluation value FV acquired at the acquisition lens position fp' at the previous time, or if the focus evaluation value FV acquired at the acquisition lens position fp' at the present time is not smaller than the focus evaluation value FV acquired at the acquisition lens position fp' at the previous time twice in series, it is judged as "No" and the processing flow returns to the scanning start processing and the processings of S.51, S.59 to S.62 are repeated.
- the CPU 8 performs the lens stop switching processing (S.64). Thereby, the pulse motor is once stopped and the evaluation value interrupt inhibit processing is performed (S.65) and then the processing flow returns to the scanning processing shown in FIG.9.
- the processings of S.51, S.59 to S.62 are processings used when reliability of the predicted focus lens position fp" is low.
- the present invention is applicable even if user of the digital still camera uses a distance or a lens position manually specified by a specifying device as the target lens position AFfp.
- a relationship between a distance to the subject the lens position fp of the focus lens fL is adjusted when the digital still camera is manufactured and the date is stored in a not-illustrated nonvolatile memory in a body.
- the lens position based on the distance specified by the user is used as the target lens position AFfp and the scanning processing (CCDAF processing) is performed at the vicinity of the target lens position AFfp as described in Example 1.
- the present invention is applicable to an electronic imaging apparatus and a digital still camera.
- the focus evaluation value generating device since the focus evaluation value generating device generates a focus evaluation value based on image data acquired through a focus lens to determine a focus lens position to a subject, and acquiring lens positions for acquiring a plurality of focus evaluation values between the present lens position of the focus lens and the target lens position are determined, there are advantageous effects in that overrun of the focus lens can be prevented before happens, that is, it can be prevented that during scanning for acquiring the focus evaluation value, the end lens position of the focus lens after the focus evaluation value is acquired exceeds the optimum focus lens position corresponding to the peak value. There may be also advantageous effect in that the overrun amount of the focus lens is reduced and sets in a range without problems on focusing.
- the target lens position of the focus lens to the subject is determined, and the acquisition lens position for acquiring the focus evaluation value (that is, for sampling the focus evaluation value) is determined based on the target lens position, probability for preventing overrun of the focus lens, that is, preventing the end lens position of the focus lens after acquiring the focus evaluation value during scanning for acquiring the focus evaluation values from exceeding the optimum focus lens position corresponding to the peak value is further increased.
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Abstract
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JP2010003605A JP5445150B2 (en) | 2010-01-12 | 2010-01-12 | Automatic focusing control device, electronic imaging device and digital still camera |
PCT/JP2011/050613 WO2011087115A1 (en) | 2010-01-12 | 2011-01-11 | Auto-focus controlling apparatus, electronic imaging apparatus and digital still camera |
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JP6171273B2 (en) | 2012-06-21 | 2017-08-02 | リコーイメージング株式会社 | Autofocus device and digital camera |
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JP5750558B2 (en) * | 2013-02-14 | 2015-07-22 | 富士フイルム株式会社 | Imaging apparatus and focus control method |
JP6345919B2 (en) * | 2013-08-27 | 2018-06-20 | オリンパス株式会社 | Imaging apparatus and camera system |
JP2018036507A (en) | 2016-08-31 | 2018-03-08 | キヤノン株式会社 | Lens controller and control method thereof |
JP6877920B2 (en) * | 2016-08-31 | 2021-05-26 | キヤノン株式会社 | Lens control device, its control method |
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CN108600638B (en) * | 2018-06-22 | 2020-08-04 | 中国计量大学 | Automatic focusing system and method for camera |
JP6582317B1 (en) * | 2018-08-28 | 2019-10-02 | エスゼット ディージェイアイ テクノロジー カンパニー リミテッドSz Dji Technology Co.,Ltd | Control device, imaging device, control method, and program |
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CN113729617A (en) * | 2021-08-20 | 2021-12-03 | 北京鹰瞳科技发展股份有限公司 | Control method and control device for lens of fundus camera |
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